Methods and apparatus for minimally invasive modular interbody fusion devices

ABSTRACT

A modular interbody fusion device for fusing adjacent spinal vertebrae that is adapted to be implanted in a prepared interbody space including a first modular segment having a width including a first rail extending at least partially along one side of the width and beyond a periphery of a body portion of the first modular segment, a second modular segment having a width and slidably connected to the first rail on one side of the width and having a second rail extending at least partially along another side of the width and beyond a periphery of a body portion of the second modular segment, a third modular segment having a width and slidably connected to the second rail on one side of the width and wherein the device has an expanded position and an implanted position in which the modular segments are combined to mimic the shape of the vertebra.

RELATED APPLICATION

The present application claims the benefit of U.S. ProvisionalApplication No. 60/860,329 filed Nov. 21, 2006, which is incorporatedherein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates generally to an implantable orthopedicfusion device for fusing joints in a patient such as a vertebralinterbody fusion device. More particularly, the present inventionrelates to a rail-based modular interbody fusion device of predeterminedsize and shape.

BACKGROUND OF THE INVENTION

Joint fusion or arthrodesis is a common approach to alleviate the paindue to deteriorated and/or arthritic joints. Joint fusion involvesinducing bone growth between two otherwise mobile bones in a joint,which alleviates pain by immobilizing and stabilizing the joint. Thejoint is generally fused in its most functional position. The ankle,wrist, finger, toe, knee and vertebral joints are all examples of jointsthat may be fused to alleviate pain associated with unstable,deteriorated joints.

The spinal motion segment consists of two adjacent vertebral bodies, theinterposed intervertebral disc, as well as the attached ligaments,muscles, bony processes and the facet joints. The disc consists of theend plates at the surfaces of the vertebral bones, the soft inner core,called the nucleus pulposus and the annulus fibrosus ligament thatcircumferentially surrounds the nucleus and connects the vertebraetogether. In normal discs, the nucleus cushions applied loads, thusprotecting the other elements of the spinal motion segment. The nucleusin a normal disc responds to compression forces by bulging outwardagainst the vertebral end plates and the annulus fibrosus. The annulusconsists of collagen fibers and a smaller amount of elastic fibers, bothof which are effective in resisting tension forces. However, the annuluson its own is not very effective in withstanding compression and shearforces.

As people age the intervertebral discs often degenerate naturally.Degeneration of the intervertebral discs may also occur in people as aresult of degenerative disc disease. Degenerative disc disease of thespine is one of the most common conditions causing back pain anddisability in our population. When a disc degenerates, the nucleusdehydrates. When a nucleus dehydrates, its ability to act as a cushionis reduced. Because the dehydrated nucleus is no longer able to bearloads, the loads are transferred to the annulus and to the facet joints.The annulus and facet joints are not capable of withstanding theirincreased share of the applied compression and torsional loads, and assuch, they gradually deteriorate. As the annulus and facet jointsdeteriorate, many other effects ensue, including the narrowing of theinterspace, bony spur formation, fragmentation of the annulus, fractureand deterioration of the cartilaginous end plates, and deterioration ofthe cartilage of the facet joints. The annulus and facet joints losetheir structural stability and subtle but pathologic motions occurbetween the spinal bones.

As the annulus loses stability it tends to bulge outward and may developa tear allowing nucleus material to extrude. Breakdown products of thedisc, including macroscopic debris, microscopic particles, and noxiousbiochemical substances build up. The particles and debris may producesciatica and the noxious biochemical substances can irritate sensitivenerve endings in and around the disc and produce low back pain. Affectedindividuals experience muscle spasms, reduced flexibility of the lowback, and pain when ordinary movements of the trunk are attempted.

Degeneration of a disc is irreversible. In some cases, the body willeventually stiffen the joints of the motion segment, effectivelyre-stabilizing the discs. Even in the cases where re-stabilizationoccurs, the process can take many years and patients often continue toexperience disabling pain. Extended painful episodes of longer thanthree months often leads patients to seek a surgical solution for theirpain.

Several methods have been devised to attempt to stabilize the spinalmotion segment. Some of these methods include: applying rigid orsemi-rigid support members on the sides of the motion segment; removingand replacing the entire disc with an articulating artificial device;removing and replacing the nucleus; and spinal fusion involvingpermanently fusing the vertebrae adjacent the affected disc.

Spinal fusion is generally regarded as an effective surgical treatmentto alleviate back pain due to degeneration of a disc. The fusion processrequires that the vertebral endplates be prepared by scraping thesurface of the existing vertebral bone to promote bleeding and releaseof bone growth factors, and placing additional bone or suitable bonesubstitute onto the prepared surface. Devices of an appropriate sizemade from rigid materials such as metals (including titanium andtantalum), some plastics (including polyetheretherketone (PEEK), orcarbon fiber-filled PEEK), and allograft bone (primarily from donorfemurs) are commonly inserted into the prepared disc cavity as part ofthe interbody fusion procedure to help distract and stabilize the discspace and put the vertebra into proper position while the bone growthprocess takes place. The interbody fusion procedure may be accomplishedfrom an anterior, transforaminal, or a posterior surgical approach.

Most devices used in interbody spinal fusion require a relatively largeopening that is typically larger than the dimensions of the rigid andunitary fusion device or cage that is to be inserted, examples of suchdevices include, U.S. Pat. No. 5,026,373 to Ray et al., U.S. Pat. No.5,458,638 to Kuslich et al., and the NOVEL™ PEEK Spacers from Alphatec.In fact, many methods of interbody fusion, for example the method anddevice described in U.S. Pat. No. 5,192,327 to Brantigan, requirebilateral placement of unitary devices through fairly large surgicalopenings. As with any surgical procedure, the larger the surgical accessrequired, the higher the risk of infection and trauma to the surroundinganatomy.

There exists minimally invasive spinal fusion devices such as isdisclosed in U.S. Pat. No. 5,549,679 to Kuslich and U.S. Pat. No.6,997,929 to Manzi et al. The device disclosed in the U.S. Pat. No.5,549,679 is a porous mesh bag that is filled in situ. The U.S. Pat. No.6,997,929 is directed to a series of wafers that are vertically stackedto distract and support the vertebral endplates. U.S. Pat. No. 5,702,454to Baumgartner discloses plastic beads which may be inserted one at atime into an intervertebral space on a flexible string. Further, U.S.Pat. No. 5,192,326 to Bao discloses hydrogel beads encased in asemi-permeable membrane.

While such minimally invasive technologies permit smaller accessincision through the annulus (i.e. an annulotomy) to be used in a fusionprocedure, the resulting fusion devices do not have the mechanical anddimensional features of the more rigid unitary fusion devices used intraditional surgical approaches and are less able to distract andstabilize the disc space. Thus, there is a need for a minimally invasivespinal fusion implant that could better emulate the mechanical andstructural characteristics of a rigid unitary fusion device.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for a rail-basedmodular interbody fusion device having a predetermined size and shapewhen assembled in situ. In one embodiment, the modular interbody fusiondevice comprises generally solid modular segments with rails thatoperably connect adjacent modular segments. This configuration allowsthe interbody spacer to be adapted for implantation via a small accessincision or annulotomy through various surgical approaches, including aposterior or a lateral approach. In one embodiment, the rails operatewith a sliding mechanism to connect and interlock adjacent modularsegments. A stem portion of the rails that extends beyond the peripheryof the body of the prosthesis is removable after implantation such thatthe modular segments combine to form a single device with a relativelysmooth outer circumference when assembled in situ. The modular fusiondevice can be configured to provide full contact with and closely mimicthe geometry of the surfaces of the joint being fused so as to moreclosely mimic the functionality of the largest existing rigid andunitary fusion devices.

In one embodiment, an interbody modular fusion device is adapted to beimplanted in a prepared intervertebral space and includes at least threemodular segments each having a width. The first modular segment has afirst rail extending at least partially along one side of the width andbeyond a periphery of the first modular segment. The second modularsegment is slidably connected to the first rail on one side of the widthand has a second rail extending at least partially along another side ofthe width and beyond a periphery of the second modular segment. Thethird modular segment is slidably connected to the second rail on oneside of the width. The interbody fusion device has an expanded positionin which the modular segments are extended along the first and secondrails and positioned in a generally end to end configuration spacedapart by the rails prior to implantation. The interbody fusion devicealso has an implanted position in which the modular segments arepositioned in a generally side by side configuration that defines asingle assembled body having a generally continuous periphery thatgenerally corresponds to the inner boundary of the annulus.

In one embodiment, each modular segment has a compressive modulus in thesuperior to inferior direction from about 0.5-15 GPa, such that thecompressive modulus of the interbody fusion device generally correspondsto the compressive modulus of the surrounding cortical bone.

In one embodiment, locking features are provided to ensure that themodular interbody spacer is a unitary device both before and afterinsertion. To prevent the device from being separated prior toinsertion, locking features may be provided on the rigid rails toprevent modular segments from being slid back off of the rails. Thisensures that each modular segment is connected in its proper positionand in the proper order. In addition, locking features may be providedon the modular segments to lock them together upon insertion. Thisprevents individual segments from dislocating from the assembledprosthesis and migrating outside of the annulus. Further, the interbodyfusion device may include grooves, ridges, or other structures on itsouter surface to contact surrounding bone and prevent the device frommigrating out beyond the anterior limit of the intervertebral space.

Another aspect of the present invention comprises a method forimplanting an interbody spacer. Because the modular interbody spacer maybe implanted one segment at a time, a hole made in the annulus forimplantation of the prosthesis may be a fraction of the size of thedevice in its final assembled form. The first modular segment isinserted into the intervertebral space through the small hole in theannulus. The second modular segment is then slid up the first rigid railand into the intervertebral space until the second modular segmentinterlocks with the first modular segment. The tail stem of the firstrigid rail is then severed from the device. This severing may beaccomplished by simply snapping the rail off the device. Alternatively,the tail stem may be attached to the device by a screw, a bayonetmechanism, a twist lock or the like. As such, the rails may be removedfrom the device by unscrewing, or releasing the bayonet, etc. Subsequentmodular segments are slid up the adjoining rigid rail into the interbodyspace and then interlocked with the previously inserted modular segmentin a similar manner. Once all of the modular segments have been insertedand all of the tail stems severed, the modular interbody spacer is fullyinserted into the patient's interbody space.

Another aspect of the present invention provides an insertion tool thatmay be used to aid in the insertion, positioning, and rail removal ofthe modular interbody spacer. The proximal end of the tool has a handlewith an enclosed ratchet or roller mechanism attached to and in linewith the inner lumen of an elongated tube at the distal end of the toolthrough which a rail may be inserted. The elongated tube may have a slitor other openings along the length of the tube to aid in threading therails into the tube. The insertion tool may be provided with a cuttingmechanism for removing the rails from the modular segments once they arefully inserted.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIGS. 1 and 1A are top views of modular interbody spacers according toembodiments of the present invention in an inserted configuration.

FIGS. 2 and 2A are perspective views of modular interbody spacersaccording to embodiments of the present invention at a first stage ofinsertion.

FIGS. 3 and 3A are perspective views of modular interbody spacersaccording to embodiments of the present invention at a second stage ofinsertion.

FIGS. 4 and 4A are perspective views of modular interbody spacersaccording to embodiments of the present invention at a final state ofinsertion.

FIG. 5 is a perspective view of an alternate embodiment of the device.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 1A, there can be seen top views of modularinterbody spacers 100 according to embodiments of the present inventionas configured once inserted into the body. In this embodiment, modulardisc prosthesis 100 comprises first 102, second 104, third 106, andfourth 108 modular segments. Interbody spacer 100 may be comprised ofany suitable biomaterial, for example, a polymer, such as PEEK, a metal,such as titanium, trabecular metal, bone, or a resorbable material thatmay act as a scaffold for new bone growth and/or a carrier for stemcells.

Modular segments 102, 104, 106 and 108 may be inserted via a smallannulotomy from a posterior or lateral approach. Interbody spacer 100may then be constructed within the interbody space by first insertingmodular segment 102 into the interbody space, then sliding modularsegments 104, 106 and 108 along a series of rails wherein each segmentlocks with the previous segment to create an interbody spacer 100 havinga final, assembled surface area that fully contacts and supports thevertebral end plates.

Interbody spacer 100 may include locking barbs that prevent individualunits from backing out or extending beyond the anterior limit of thespacer. Spacer 100 may further include grooves, ridges 142 or otherstructures to engage the surrounding bone or otherwise prevent spacer100 from backing out of the intervertebral space.

In a preferred embodiment, interbody spacer 100 may be made of PEEKhaving holes 140 extending through the spacer allowing for tissueingrowth thus promoting bony fusion. The holes 140 may be of varyingsize and shape. Holes 140 may be spaced apart on spacer 100 in anymanner such that the compressive modulus of spacer 100 generallycorresponds to the compressive modulus of the adjacent bone. Spacer 100may also be of varying thicknesses to achieve the desired support and/orfusion of a particular intervertebral space, such as a lordoticconfiguration for L5-S1 fusion.

In an embodiment, prior to insertion, holes 140 of interbody spacer 100may be packed or filled for example with, autologous bone graft,calcified or decalcified bone derivative, bone graft substitute, such ashydroxyapatite, agents to promote bone growth, such as bonemorphogenetic protein, or osteogenic protein-1, antibiotics, anti-canceragents, stem cells, biologically active cytokines, cytokine inhibitors,fibroblast growth factors, other osteoinductive and/or osteoconductivematerials or any other material and combination thereof to promotefusion and/or stabilize the spinal motion segment.

In another embodiment, interbody spacer 100 may include surfacemodifications to provide for elution of medicants. Such medicants mayinclude analgesics, antibiotics, anti-inflammatories, anticoagulants,antineoplastics or bioosteologics such as bone growth agents. In analternative embodiment, spacer 100 may be comprised of a material, suchas for example, porous PEEK, from which an imbibed medicant can elute.In yet another embodiment, an inner portion of the spacer 100 may becomprised of one material, while the outer portion is comprised ofanother material. For example, the inner portion may be comprised of asolid PEEK, while the outer portion is comprised of a porous PEEK. Thesurface of the porous PEEK may be coated with a bioactive agent ormedicant. Spacer 100 may be imbedded with a radiopaque material, such astantalum or titanium beads to allow for x-ray visualization of theimplant.

In another embodiment, the rails may be used as fill tubes such thatfill material may be injected or otherwise inserted into holes 140.Spacer 100 may also be manufactured to include channels or ducts intowhich fill material may be inserted via the rails.

Referring to FIGS. 2 and 2A, there can be seen a portion of the modularinterbody spacers 100 according to embodiments of the present inventionprior to insertion into the intervertebral space. In alternateembodiments, the modular interbody spacer may comprise greater or fewernumbers of modular segments and rails.

Prior to insertion, modular interbody spacer 100 further includes first110, second 112, and third 114 rails. First modular segment 102 isrigidly attached to first rail 110 at first segment interlocking portion116. As shown in FIGS. 3 and 3A, second modular segment 104 is slidablyattached to first segment interlocking portion 116 at first slot 128 andrigidly attached to second rail 112 at second segment interlockingportion 118. As shown in FIGS. 4 and 4A, third modular segment 106 isslidably attached to second interlocking portion 118 at second slot 130and rigidly attached to third rail 114 at third segment interlockingportion 120. Fourth modular segment 108 is slidably attached to thirdrail 114 at fourth slot 133.

As shown in FIG. 2, each rail 110, 112 and 114 includes a stem portionthat extends beyond a periphery of the body of the spacer 100,respectively. Preferably these stem portions are long enough to permitaccess into the intervertebral space such that one modular segment canbe positioned inside the intervertebral space while the next modularsegment on the rail is still outside of the body. In an exemplaryembodiment, the length of the stem portions ranges between 6 cm-20 cm.Each rail 110, 112 and 114 may further include a retaining portion tokeep the device from being separated prior to insertion. The retainingportions are configured to prevent the corresponding modular segmentsfrom sliding off the rails. The retaining portions may be molded intothe rails or may be separate pieces or deformations of the rails addedduring the manufacture of the device. Rails 110, 112, 114 may besequentially removed from the implant as modular segments 102, 104, 106,and 108 are connected within the intervertebral space and movedlaterally.

The preferred embodiment is an interbody spacer that is packaged,sterile, and ready for implantation at the surgical site. The packagemay include any number of modular segments. In a preferred embodiment,the package would include 5 individual modular segments. Single modulepackages may also be used so that the surgeon may use as many segmentsas desired. Since the device is fully preformed and delivered as aunitary implant, the device is under direct surgeon control until theinterbody spacer is completely formed. This unitary design reduces theneed for the surgeon to determine how to configure the spacer to allowfor the most efficacious placement of the spacer in the intervertebralspace and assures that the components' order of insertion and connectionare properly achieved. The size and shape of the modular interbodyspacer provides a final, assembled surface area that fully contacts andsupports the vertebral end plates, stabilizing the spinal unit. In thisregard, it will be understood that the modular interbody spacer 100 ofthe present invention may be provided in a variety of different finalassembled sizes to correspond to different sizes of differentintervertebral spaces.

In an alternative embodiment as shown in FIG. 5, separate guide rods 150and a guide mechanism 152 may be used to assist in inserting andaligning the modular segments. Rod 150 may be attached to the proximalend of each modular segment. Rod 150 may be used to insert a firstmodular segment into position. A second guide rod may be attached to asecond modular segment and used to place the second modular segment inposition to mate and interlock with the first modular segment. The firstrod could then be detached. Subsequent segments could be inserted byrepeating the process.

In an embodiment, a modular segment may include a tapped hole 154 suchthat rod 150 may be screwed into hole 154. Rod 150 does not participatein the interlocking mechanism of modular segments. In an embodiment, rod150 may either be made of the same material as the modular segments, orrod 150 may be comprised of a different material, including, but notlimited to, plastics such as PEEK, or metals such as stainless steel ortitanium. According to one aspect of the present invention, rod 150 maybe integral to the modular segments. For example, rod 150 may beinjection molded from a plastic or machined from a plastic or metal.

In another embodiment of the present invention, rod 150 may be formedseparately from the modular segments and then joined to the modularsegments via a mechanical method such as a mating thread, twist-lock,snap-lock or such, or by the use of adhesives or other material joiningmethods such as thermal and ultrasonic welding. One advantage to using amechanical method of joining rod 150 to the modular segments is thepotential to re-engage the modular segments for removal from the discspace, should the need arise. The removal sequence of rods 150 from themodular segments following implantation of the modular segments in thedisc space is the same as for interlocking rails.

In an embodiment, modular interbody spacer 100 may be introduced throughan access tube that is inserted partially into the intervertebral space.The access tube is at least 3 inches long and preferably about 6 incheslong. It should be noted that although the insertion of modularintervertebral spacer 100 is described in relation to a four-segmentembodiment, embodiments having any other number of segments would beinserted in a similar fashion.

During insertion, slots 128, 130, 133 slide along the stem portions ofrails 110, 112, 114 and onto segment interlocking portions 116, 118,120. Slots 128, 130, 133 and segment interlocking portions 116, 118, 120may be provided with locking features to prevent separation of modularsegments 102, 104, 106 and 108. Locking features, such as a barb or studor a series of barbs or studs, may be provided such that once a slot isslid onto a segment interlocking portion, it cannot be slid back off ofit. A ratchet and pawl may also be used to lock modular segmentstogether. A ratchet release tool may also be provided in case separationof modular segments is desired once they are locked together.

Various modifications to the disclosed apparatuses and methods may beapparent to one of skill in the art upon reading this disclosure. Theabove is not contemplated to limit the scope of the present invention,which is limited only by the claims below.

The invention claimed is:
 1. A modular interbody fusion device forfusing adjacent spinal vertebrae and adapted to be implanted in aprepared interbody space defined between a first vertebral endplate anda second vertebral endplate, the fusion device having an expandedposition before implantation and an implanted position afterimplantation, the device comprising: a plurality of modular segmentsformed of an inert biomaterial such that each modular segment includes asuperior surface and an inferior surface defined by the inertbiomaterial and separated by a respective thickness, each superiorsurface being configured to contact the first vertebral endplate andeach inferior surface being configured to contact the second vertebralendplate, the plurality of modular segments including structure adaptedto allow tissue ingrowth, the structure defining a hole that passesthrough the inert biomaterial of the superior surface and the inertbiomaterial of the inferior surface of at least one of the modularsegments and that, when in the implanted position, are arranged side byside from a first end of the device to a second end of the device, theplurality of modular segments being configured for assembly in sequencefrom the first end to the second end of the device and cooperating witheach other when in the implanted position to define a rigid unitary bodyhaving a periphery that generally corresponds to the prepared interbodyspace and is configured such that the inert biomaterial of the superiorsurface and the inferior surface is configured to contact the first andsecond vertebral endplates respectively; a first of the plurality ofmodular segments being rigidly attached to a fixed end of a first rail,the first rail including a free end opposite the fixed end of the firstrail; a second of the plurality of modular segments being rigidlyattached to a fixed end of a second rail and being slidably connected tothe first rail, the second rail including a free end opposite the fixedend of the second rail; a third of the plurality of modular segmentsadapted to slidably connect with the second rail, each of the first andsecond rails including a stem portion that extends beyond the peripheryof the unitary body when in the implanted position, the stem portion ofthe first rail being selectively removable from the first rail once thesecond modular segment is in the implanted position, the stem portion ofthe second rail being selectively removable from the second rail oncethe third modular segment is in the implanted position, the secondmodular segment, when in the expanded position, being extended along thestem portion of the first rail, so that the first and second modularsegments are positioned in a generally end to end configuration spacedapart by the stem portion of the first rail prior to implantation of thesecond modular segment; and an insertion tool for inserting the secondmodular segment along the first rail and the third modular segment alongthe second rail, the insertion tool including a separation mechanism toremove the stem portion of the first rail and the stem portion of thesecond rail following assembly of the rigid unitary body.
 2. The modularinterbody fusion device of claim 1, wherein the third modular segment isrigidly attached to a third rail and the modular interbody fusion devicefurther comprises a fourth of the plurality of modular segments adaptedto slidably connect with the third rail and to be inserted with the aidof the insertion tool.
 3. The modular interbody fusion device of claim2, wherein the fourth modular segment is rigidly attached to a fourthrail and the modular interbody fusion device further comprises a fifthof the plurality of modular segments adapted to slidably connect withthe fourth rail and to be inserted with the aid of the insertion tool.4. The modular fusion device of claim 1, wherein the modular segmentsfurther comprise means for interlocking adjacent ones of the modularsegments in the implanted position.
 5. The modular fusion device ofclaim 1, wherein each rail further includes means for retaining theslidably attached modular segment on the rail in the expanded position.6. The modular fusion device of claim 1, wherein each of the modularsegments are of a similar width transverse to the respective thicknessto define a width of the device in the expanded position that determinesa minimum width of an opening for insertion of the device into theinterbody space.
 7. The modular fusion device of claim 1, wherein thethickness of the modular segments varies based on the prepared interbodyspace.
 8. The modular interfusion device of claim 1 wherein the modularinterbody fusion device is adapted for one of a lateral surgicalapproach and a posterior surgical approach.
 9. The modular interbodyfusion device of claim 1, wherein the inert biomaterial comprises PEEK.10. A method of providing a modular fusion device for fusing a spinaljoint, the method comprising: providing a plurality of modular segmentsformed from an inert biomaterial such that each modular segment includesa superior surface and an inferior surface defined from the inertbiomaterial, each superior surface being configured to contact a firstvertebral endplate and each inferior surface being configured to contacta second vertebral endplate, the plurality of modular segments includingstructure adapted to allow tissue ingrowth, the structure defining ahole that passes through the inert biomaterial of the superior surfaceand the inert biomaterial of the inferior surface of at least one of themodular segments, the segments adapted to form an implanted modularfusion device having a periphery that is configured to contact the jointto be fused, a first of the plurality of modular segments being rigidlyattached to a fixed end of a first rail, a second of the plurality ofmodular segments being rigidly attached to a fixed end of a second rail,the first rail and the second rail each having a free end opposite therespective fixed end; providing instructions for implanting the modularfusion device, the instructions comprising: inserting the first modularsegment into an interbody space through an opening so that the firstrail extends out of the interbody space when the first modular segmentis located within the interbody space; sliding the second modularsegment along the first rail into the interbody space through theopening using an insertion tool until the second modular segmentcontacts and interlocks with the first modular segment so that thesecond rail extends out of the interbody space when the second modularsegment is located within the interbody space; removing a portion of thefirst rail that extends from the interlocked first and second modularsegments with a separation mechanism provided at a distal end of theinsertion tool; sliding a third of the plurality of modular segmentsalong the second rail into the interbody space through the opening usingthe insertion tool until the third modular segment contacts andinterlocks with the second modular segment; and removing a portion ofthe second rail that extends from the interlocked second and thirdmodular segments with the separation mechanism to form an implantedmodular fusion device having a periphery that is configured to contactthe joint to be fused such that the inert biomaterial is in full contactwith the first and second vertebral endplates.
 11. The method of claim10, wherein the third modular segment provided in the step of providinga plurality of modular segments is rigidly attached to a third rail thatextends out of the interbody space when the third modular segment islocated within the interbody space, the instructions provided in thestep of providing instructions further comprising: sliding a fourth ofthe plurality of modular segments along the third rail into theinterbody space through the opening using the insertion tool until thefourth modular segment contacts and interlocks with the third modularsegment; and removing a portion of the third rail that extends from theinterlocked third and fourth modular segments with the separationmechanism.
 12. The method of claim 11, wherein the fourth modularsegment provided in said step of providing a plurality of modularsegments is rigidly attached to a fourth rail that extends out of theinterbody space when the fourth modular segment is located within theinterbody space, the instructions provided in the step of providinginstructions further comprising: sliding a fifth of the plurality ofmodular segments along the fourth rail into the interbody space throughthe opening using the insertion tool until the fifth modular segmentcontacts and interlocks with the fourth modular segment; and removing aportion of the fourth rail that extends from the interlocked fourth andfifth modular segments with the separation mechanism.
 13. The method ofclaim 10 wherein the step of inserting is performed from a lateralsurgical approach or a posterior surgical approach.
 14. The method ofclaim 10, wherein the inert biomaterial comprises PEEK.
 15. A minimallyinvasive method of implanting a modular fusion device in a preparedinterbody space for fusing a spinal joint, the method comprising:providing a plurality of modular segments formed of an inert biomaterialsuch that each modular segment includes a superior surface and aninferior surface formed of the inert biomaterial, each superior surfacebeing configured to contact a first vertebral endplate and each inferiorsurface being configured to contact a second vertebral endplate, theplurality of modular segments including structure adapted to allowtissue ingrowth, the structure defining a hole that passes through theinert biomaterial of the superior surface and the inert biomaterial ofthe inferior surface of at least one of the modular segments, theplurality of modular segments cooperating with each other when in animplanted position to define a unitary body having a periphery thatgenerally corresponds to the prepared interbody space and is configuredsuch that the inert biomaterial is configured to contact the first andsecond vertebral endplates; providing a first of the plurality ofmodular segments rigidly attached to a fixed end of a first rail, thefirst rail having a free end opposite the fixed end of the first railthat extends out of the interbody space when the first modular segmentis located within the interbody space; providing a second of theplurality of modular segments rigidly attached to a fixed end of asecond rail, the second rail having a free end opposite the fixed end ofthe second rail that extends out of the interbody space when the secondmodular segment is located within the interbody space; inserting thefirst of the plurality of modular segments into the interbody spacethrough an opening; sliding the second of the plurality of modularsegments along the first rail into the interbody space through theopening using an insertion tool until the second modular segmentcontacts and interlocks with the first modular segment; removing aportion of the first rail that extends from the interlocked first andsecond modular segments with a separation mechanism provided at a distalend of the insertion tool; sliding a third of the plurality of modularsegments along the second rail into the interbody space through theopening using the insertion tool until the third modular segmentinterlocks with the second modular segment; and removing a portion ofthe second rail that extends from the interlocked second and thirdmodular segments with the separation mechanism to form an implantedmodular fusion device having a periphery that is configured to contactthe joint to be fused.
 16. The method of claim 15 wherein the modularsegments provided in the steps of inserting are adapted for one of alateral surgical approach and a posterior surgical approach.
 17. Theminimally invasive method of claim 15, wherein the inert biomaterialcomprises PEEK.
 18. A modular interbody fusion device for fusingadjacent spinal vertebral endplates that is adapted to be implanted in aprepared interbody space, the device comprising: a first modular segmentformed of an inert biomaterial such that each modular segment has awidth including a first rail having a fixed end that extends at leastpartially along one side of the width, the first rail including a freeend opposite the fixed end of the first rail, the first rail extendingbeyond a periphery of a body portion of the first modular segment; asecond modular segment formed of the inert biomaterial, the secondmodular segment having a width and slidably connected to the first railon one side of the width and having a second rail having a fixed endthat extends at least partially along another side of the width, thesecond rail including a free end opposite the fixed end of the secondrail, the second rail extending beyond a periphery of a body portion ofthe second modular segment; and a third modular segment formed of theinert biomaterial, the third modular segment having a width and slidablyconnected to the second rail on one side of the width, wherein thedevice has an expanded position in which the second and third modularsegments are extended along the first and second rails and positioned inan end to end configuration spaced apart by the rails prior toimplantation and an implanted position in which the modular segments arepositioned in a side by side configuration that defines a unitary bodythat is configured to contact the vertebral endplates, each modularsegment having a superior surface formed of the inert biomaterialconfigured to contact a first vertebral endplate and an inferior surfaceformed of the inert biomaterial configured to contact a second vertebralendplates such that the inert biomaterial is configured to be in contactwith the first and second vertebral endplates; wherein the deviceincludes an insertion tool for inserting the second modular segmentalong the first rail and the third modular segment along the secondrail, the insertion tool including a separation mechanism to remove astem portion of the first rail and a stem portion of the second railfollowing assembly of the unitary body, wherein the stem portion of thefirst rail and the stem portion of the second rail extends beyond theunitary body wherein at least one of the modular segments includesstructure for allowing tissue ingrowth, the structure defining a holethat passes through the inert biomaterial of the superior surface andthe inert biomaterial of the inferior surface of at least one of themodular segments.
 19. The modular interbody fusion device of claim 18,wherein the inert biomaterial comprises PEEK.